The invention relates generally to suspension locking of work vehicles. More particularly it relates to automatic suspension locking of skid steer vehicles when the vehicle turns above a threshold turning rate.
Skid steer loaders are small highly maneuverable vehicles that are used in place of front end loaders, backhoes and the like in constricted environments. They are particularly useful due to their small size and maneuverability.
Their maneuverability is due to their method of steering. The wheels on one side of the vehicle (typically two per side) can be driven independently of the wheels on the other side of the vehicle. The wheels themselves are not steerable. In other words, they cannot be turned about a generally vertical axis with respect to the chassis.
To steer a skid steer vehicle, the wheels on one side of the vehicle are driven at a different speed than the wheels on the other side of the vehicle. In an extreme case they are also driven in opposite directions. Thus, the wheels on one side can be driven forward as the wheels on the other side of the chassis are driven in reverse.
These different velocities cause the wheels to skid sideways as they rotate. As a result, one side of the vehicle advances faster than the other, and the vehicle turns. In the extreme case, when the wheels on either side are driven in opposite directions, the vehicle can rotate about a vertical axis within the perimeter of the vehicle""s chassis thereby giving it a turning radius of zero.
In addition to the maneuverability provided by the steering arrangement, skid steer vehicles also benefit from a narrow wheelbase and small width over wheels. A short wheelbase and small width over wheels permits the vehicle to be used in confined spaces, but prevents the use of sprung suspensions.
A sprung suspension used on a short wheelbase vehicle such as a skid steer loader would significantly reduce ground clearance while turning at speed due to the compression of the outboard (i.e. on the outside of the turn) wheels"" compression in response to the centrifugal forces generated during turning. This could cause a collision between the bottom of the vehicle and the ground or dumping of the load carried in the bucket of the loader, if so equipped.
One of the factors determining the degree of compression of the outboard suspensions is the turning radius of the vehicle. It is the turning radius that defines the path followed by the vehicle and hence the centrifugal force experienced by that vehicle. The centrifugal force is proportional to the lateral acceleration of the vehicle as it makes the turn. By xe2x80x9clateral accelerationxe2x80x9d we refer to the side-to-side acceleration of the vehicle, which is perpendicular to the direction of the vehicle""s forward (or backward, if going in reverse) travel.
The turning radius of skid steer vehicles can be quite small since a skid steer vehicle an drive the wheels on either side of the chassis independently, and even in opposite directions. Automobiles and other work vehicles with steerable front wheels have typical minimum turning radii of 30 feet. Skid steer vehicles (depending upon their load) have minimum turning radii on the order of a few inches.
Given skid steer vehicles"" relatively small turning radius as compared to other work vehicles such as front loaders, the centrifugal forces experienced by skid steer vehicles are considerable and would cause significant compression of an outboard suspension.
Further complicating the problems inherent in skid steer loaders due to their method of turning are problems due to their short wheelbase and width over wheels combined with the high lift of their loader arms. Skid steer vehicles equipped with loader arms and buckets are at particular risk when the loader arms are raised and the arms are supporting a significant weight. On many skid steer loaders, the loader arms and bucket can be raised more than twice as high as the wheelbase is long. If the bucket is loaded, this height can significantly raise the center of gravity, a particular problem when the vehicle experiences centrifugal forces during acceleration.
These problems indicate that some system of resisting centrifugal forces and preventing the rolling of a skid steer vehicle having sprung suspensions would be beneficial. It is an object of this invention to provide such a system for use in a skid steer vehicle.
In accordance with a first embodiment of the present invention, A skid steer vehicle is provided that includes a chassis having a left side and a right side; at least one loader arm pivotally coupled to the chassis to pivot about a substantially horizontal axis; at least one hydraulic cylinder coupled to the at least one loader arm to raise and lower the at least one loader arm with respect to the chassis; an engine coupled to the chassis; first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure; four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation; four control arms pivotally coupled to the chassis and coupled to the four wheels to permit the wheels to pivot at least in a vertical direction with respect to the chassis; at least two hydraulic motors for driving the wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis; four hydraulic cylinders, each cylinder operably coupled to one of the wheels to control at least the vertical position of the wheels with respect to the chassis; a means for indicating the lateral acceleration of the vehicle; and an electronic controller operably coupled to the means for indicating and responsive to the means for indicating to (a) lock two wheels of the four wheels on the left side of the vehicle when the vehicle experiences rightward acceleration greater than a predetermined level of lateral acceleration, and (b) to lock two wheels of the four wheels on the right side of the vehicle when the vehicle experiences leftward acceleration greater than the predetermined level of lateral acceleration.
The means for indicating may include a satellite positioning receiver, an accelerometer, at least two wheel speed sensors, first and second specific displacement sensors respectively indicative of the displacement of the first and second hydraulic pumps, or memory locations in the electronic controller containing data indicative of commanded displacements of the first and second hydraulic pumps. The means for indicating may include the satellite positioning receiver configured to provide a signal indicative of lateral vehicle acceleration, wherein the electronic controller is configured to receive the signal indicative of lateral acceleration and to compare that signal with a predetermined value indicative of lateral acceleration and to lock the two wheels on the side of the vehicle that would otherwise be compressed by centrifugal force during turning. The means for indicating may include the accelerometer configured to provide a signal indicative of lateral vehicle acceleration, wherein the electronic controller is configured to receive the signal indicative of lateral acceleration from the accelerometer, to compare that signal indicative of lateral acceleration with a predetermined value indicative of lateral acceleration and to lock the two wheels on the side of the vehicle that would otherwise be compressed by centrifugal force during turning. The means for indicating may include the at least two wheel speed sensors configured to indicate the respective speed of two wheels including a first wheel on the left side of the vehicle and a second wheel on the right side of the vehicle, and further wherein the electronic controller is configured to receive and combine the respective speeds from the wheel speed sensors to provide a value indicative of lateral acceleration, to compare the value indicative of lateral acceleration with a predetermined value indicative of lateral acceleration, and to lock the two wheels on the side of the vehicle that would otherwise be compressed by centrifugal force during turning when that predetermined value indicative of lateral acceleration is exceeded. The means for indicating may include the first and second specific displacement sensors configured to indicate the respective specific displacements of the first and second variable displacement hydraulic pumps, wherein the electronic controller is configured to receive and combine signals from the first and second specific displacement sensors to provide a value indicative of lateral acceleration, to compare the value indicative of lateral acceleration with a predetermined value indicative of lateral acceleration, and to lock the two wheels on the side of the vehicle that would otherwise be compressed by centrifugal force during turning when that predetermined value indicative of lateral acceleration is exceeded. The means for indicating may include the at least two specific displacement sensors configured to indicate the respective specific displacements of the first and second variable displacement hydraulic pumps, wherein the electronic controller is configured to receive and combine signals from the two specific displacement sensors to provide a value indicative of lateral acceleration, to compare the value indicative of lateral acceleration with a predetermined value indicative of lateral acceleration, and to lock the two wheels on the side of the vehicle that would otherwise be compressed by centrifugal force during turning when that predetermined value indicative of lateral acceleration is exceeded. The means for indicating may include the memory locations in the electronic controller containing data indicative of commnanded displacements of the first and second hydraulic pumps, wherein the electronic controller is configured to retrieve commanded specific displacement values from the memory locations, to combine the commanded specific displacement values to provide a value indicative of lateral acceleration, to compare the value indicative of lateral acceleration with a predetermined value indicative of lateral acceleration, and to lock the two wheels on the side of the vehicle that would otherwise be compressed by centrifugal force during turning when that predetermined value indicative of lateral acceleration is exceeded. The commanded specific displacement values may be values indicative of swash plate positions of the first and second pumps that were previously generated and stored in the memory locations by the electronic controller. The values indicative of swash plate positions may have been previously applied by the electronic controller to the first and second pumps to vary the specific displacement of those pumps.